1. Field of the Invention
This invention relates to a radiation image storage panel and more particularly, to a radiation image storage panel comprising a support and a phosphor layer provided thereon which comprises a binder and a stimulable phosphor dispersed therein.
2. Description of Prior Arts
For obtaining a radiation image, there has been conventionally employed a radiography utilizing a combination of a radiographic film having an emulsion layer containing a photosensitive silver salt material and a radiographic intensifying screen.
As a method replacing the above-described radiography, a radiation image recording and reproducing method utilizing a stimulable phosphor as described, for instance, in U.S. Pat. No. 4,239,968, has been recently paid much attention. In the radiation image recording and reproducing method, a radiation image storage panel comprising a stimulable phosphor (i.e., stimulable phosphor sheet) is used, and the method involves steps of causing the stimulable phoshor of the panel to absorb radiation energy having passed through an object or having radiated from an object; exciting the stimulable phosphor with an electromagnetic wave such as visible light and infrared rays (hereinafter referred to as "stimulating rays") to sequentially release the radiation energy stored in the stimulable phosphor as light emission (stimulated emission); photoelectrically converting the emitted light to give electric signals; and reproducing the electric signals as a visible image on a recording material such as a photosensitive film or on a displaying device such as CRT.
In the above-described radiation image recording and reproducing method, a radiation image can be obtained with a sufficient amount of information by applying a radiation to the object at considerably smaller dose, as compared with the case of using the conventional radiography. Accordingly, this radiation image recording and reproducing method is of great value especially when the method is used for medical diagnosis.
The radiation image storage panel employed in the above-described radiation image recording and reproducing method has a basic structure comprising a support and a phosphor layer provided on one surface of the support. Further, a transparent film is generally provided on the free surface (surface not facing the support) of the phosphor layer to keep the phosphor layer from chemical deterioration or physical shock.
The phosphor layer comprises a binder and stimulable phosphor particles dispersed therein. The stimulable phosphor emits light (stimulated emission) when excited with stimulating rays after having been exposed to a radiation such as X-rays. Accordingly, the radiation having passed through an object or having radiated from an object is absorbed by the phosphor layer of the radiation image storage panel in proportion to the applied radiation dose, and a radiation image of the object is produced in the radiation image storage panel in the form of a radiation energy-stored image (latent image). The radiation energy-stored image can be released as stimulated emission (light emission) by applying stimulating rays to the panel, for instance, by scanning the panel with stimulating rays. The stimulated emission is then photoelectrically converted to electric signals, so as to produce a visible image from the radiation energy-stored image.
It is desired for the radiation image storage panel employed in the radiation image recording and reproducing method to have a high sensitivity and to provide an image of high quality (high sharpness, high graininess, etc.).
For enhancing the sensitivity of a radiation image storage panel, it has been known that a light-reflecting layer is provided between the support and the phosphor layer, for instance, by vapor-depositing a metal such as aluminum on the support, laminating a metal foil such as an aluminum foil thereon or coating it with a dispersion comprising a binder and a white pigment to form a light-reflecting layer, and subsequently forming the phosphor layer on the light-reflecting layer. A radiation image storage panel having the light-reflecting layer containing a white pigment is disclosed in Japanese Patent Provisional Publication No. 56(1981)-12600 (corresponding to U.S. Pat. No. 4,380,702).
For enhancing the sharpness of an image provided by a radiation image storage panel, it has been known to color the panel with a colorant capable of absorbing at least a portion of stimulating rays for a stimulable phosphor contained therein. A radiation image storage panel colored with such colorant is disclosed, for instance, in Japanese Patent Provisional Publication No. 55(1980)-163500 (corresponding to U.S. Pat. No. 4,394,581 and European Patent Publication No. 21174).
Further, in order to obtain a radiation image storage panel providing an image of higher sharpness than that provided by the radiation image storage panel having the light-reflecting layer containing a white pigment when the comparison is made on the same sensitivity level basis, it has been known to provide a white pigment light-reflecting layer between the support and the phosphor layer and to color the portion of the panel which is positioned on the stimulating rays-incident side with respect to the light-reflecting layer with such a colorant as mentioned above. For example, at least one of a subbing layer, a phosphor layer and a protective film is colored in the case that a panel comprises a support, a white pigment light-reflecting layer, the subbing layer, the phosphor layer and the protective film, superposed in this order. Such a radiation image storage panel is also disclosed in the above-mentioned Japanese Patent Provisional Publication No. 56(1980)-12600.
A radiation image storage panel employed in the radiation image recording and reproducing method, as described above, is desirable to have a higher sensitivity and to provide an image more improved in the quality, especially for applying the method to medical diagnosis. Accordingly, a further improvement in the sensitivity of a radiation image storage panel and the quality of the image provided thereby is desired.